1. Field of the Invention
The invention relates to ceramic linings a insulating of metallic walls of combustion chambers.
2. Discussion of Background
A ceramic lining of the type mentioned at the beginning is known from DE 195 02 730 A1. The lining there has the purpose of an uncooled detachable lining of a combustion space with ceramic elements which withstand the high mechanical and thermal stresses in a commercial heavy-duty combustion chamber.
For this purpose, the lining comprises at least one wall panel, made of refractory structural ceramic and having at least one through-opening, and a fastening element per opening. The fastening element is fastened by its foot in a metallic holding device fastened on the metallic supporting wall. The head of the fastening element rests in the opening in the wall panel. Arranged between the metallic wall and the ceramic wall panel is an insulating layer. The fastening element consists of refractory structural ceramic and is resiliently coupled to the holding device. Regarded as the advantages are that the lining can withstand very high mechanical and thermal stresses on account of its homogeneity and the material used and that the lining can be disassembled without being destroyed and can therefore be used repeatedly. Furthermore, the resilient coupling of the ceramic structure to the metallic holding construction allows the thermal expansions between metallic and ceramic components or deformations of the insulating layer due to mechanical stresses to be absorbed. It is considered particularly expedient for the fastening element to have a thermically optimized form, preferably a concavity in the center of the head, a rounded-off head and rounded-off cross-sectional transitions with large radii from the head to the shank and from the shank to the foot. This achieves the effect that the mechanically and thermally induced loads cause only minor stresses.
In the case of this known lining, a surface contact was chosen between the component to be fastened and the component via which the pressing force is introduced. For this purpose, the seat of the bolt on the tile is designed as a ball/ball seat. One of the reasons for this is to ensure a pendulum motion of the bolt free from any bending moments, since said bolt can get into a skewed position as a result of production and assembly inaccuracies and/or also due to operationally caused displacements of the components.
In the ideal case, when the ball diameter of the bolt corresponds precisely to that of the tile, there is negligible Hertzian stress at the contact surface. If, however, the two ball diameters involved deviate from each other, which may be the consequence of production tolerances and/or thermal expansions, there is immediately just linear contact of the two components at one edge of the tile-ball seat. The ball seat terminates via radii at its ends. As a result, with the differences in diameter mentioned there are immediately two convex surfaces facing each other. This leads to very high undesired Hertzian stresses.